Automotive AC dehumidifier Cross-breed heat pump

[ecomodded]

I have non functioning AC in my car that I want to remove , I also have a need for some free or recycled components for a dehumidifier based heat pump.

I will be removing the car's large near 3 ft x 2 ft ac condenser that is mounted in front of the car radiator, I think it will work well as the condenser in the heat pump build , do to its large area.

The car also has a evaporator mounted under the dash that I can salvage if need be, although it appears smallish in scale compared to the condenser , it's thicker and should be ? plenty large for the dehumidifiers compressor I deduce.

I will pull the parts off the car in next couple of days and see what I have to work with.
Any advice would be great as you may foresee some issues or methods I might be interested in.

I will add pictures when the parts come off.

[AC_Hacker]

Originally Posted by ecomodded

I have non functioning AC in my car that I want to remove , I also have a need for some free or recycled components for a dehumidifier based heat pump.

I will be removing the car's large near 3 ft x 2 ft ac condenser that is mounted in front of the car radiator, I think it will work well as the condenser in the heat pump build , do to its large area.

The car also has a evaporator mounted under the dash that I can salvage if need be, although it appears smallish in scale compared to the condenser , it's thicker and should be ? plenty large for the dehumidifiers compressor I deduce.

I will pull the parts off the car in next couple of days and see what I have to work with.
Any advice would be great as you may foresee some issues or methods I might be interested in.

I will add pictures when the parts come off.

I wish you success on your project, and I am interested to see how it turns out.

I would have to say, however, that I have suspected that auto compressors are likely to be lower in efficiency (compared to hermetically sealed compressors), because they have such a huge source of motive force available (the engine of the car), that the fine points of efficiency might have been overlooked in the design of the compressor.

There is also the potential loss from your electric motor to the compressor. Belt drive would be pretty inefficient. Chain drive would be more efficient, but also more noisy. Direct coupling to the compressor would be the most efficient, and most quiet, but you need to allow some degree of flex, to allow for imperfections in alignment, etc. So a flex coupling would be needed.

Another potential issue is eventual refrigerant leakage from the compressor. As far as I know, auto compressors use some kind of seal that ultimately results in friction around the shaft. And the seals will wear in time and leak. If I'm not mistaken, car A/C systems are the largest source of escaped refrigerant leakage.

Hermetically sealed compressors (first introduced in 1938), such as those found in de-humidifiers, air conditioners, refrigerators, etc. have solved the compressor drive problem by integrating the motor onto the same shaft as the compressor. Also the motor and compressor are inside a hermetically sealed enclosure, which eliminates the need for seals, as the whole enclosure is the seal.

Another potential concern is the condenser heat exchanger. I am not a HVAC design engineer, but I would guess that the people who are, would take advantage of the fact that a car A/C system will be operating with a 40 mph to 80 mph wind to help remove heat from the condenser, so they wouldn't tend to focus their design on low-velocity air movement, and the HX design considerations that low-velocity air might demand.

But, these are only my suspicions, and my assumptions, and I have no proof that any of them are true.

So, I am very interested to see how your project turns out.

Best of luck!

-AC_Hacker

[ecomodded]

I plan to use the dehumidifiers compressor the cars condenser and possible its evaporator as well.

The cars compressor will be left in place for its pulley as its used to line up the serpentine belt with other components. One day I may add a AC delete pulley and ditch the compressor completely.

[ecomodded]

thanks for the well wishes AC_Hacker

I am thinking if not hoping the dehumidifiers low power compressor combined with the car's large condenser will help elevate frost build up.
I will look deeper into the reversing valve and frost thermostat and employ them to defrost in cold weather.

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A few questions I have off the top of my hat are:

Once its built can I pressure test my brazing with compressed air ?.. since its just a cheapo system..

What *affordable* refrigerant can I use , if any, in place of the R134a used by dehumidifier's compressor currently ?

Compressor # LG NR58HAQG

Motor type : RSIR, PTC
Displacement : 58

[NiHaoMike]

R152a is commonly found in air dusters (look for "difluoroethane" on the label) and works very well.

A/C RECHARGE WITH COMPUTER AIR DUSTER !!! - YouTube

[ecomodded]

What a good tip NiHaoMike its affordable readily available and ozone safe.
A great idea / substitute for the R134a ,it's Perfect for this project.

Tomorrows forecast has a break in the rain and some sunshine I will take that opportunity to remove the condenser.

[jeff5may]

I found some performance data on your cited compressor.

In its typical (dehumidifier) setup, it uses 350 watts of power while moving 2382 btu/hr (698W). The model number indicates 5.8 cc of displacement.

The dehumidifier I took some pics of in my "frost control" thread has about the same size LG compressor in it. The number is QA064CAB. It uses R22, so the capacity is a little higher, around 4000 btu/hr. I disemboweled the goldstar unit just like it, and it did just fine using both heat exchangers together. I learned a lot about the entire process with it, and ended up doing a "hot gas bypass" for defrosting it.

If you run an automotive condenser coil as an evaporator with its electric DC fan, you will most likely be able to reduce its speed considerably. If it were mine, I would plumb the two heat exchangers in the dehumidifier in series and run them off the dehumidifer fan as a condenser... This should get you a hundred or more extra watts of heat flow, raising your COP up to close to 3. You would need to adjust (shorten) the cap tube to match the added heat flow. If you ran a TXV, maybe 1/3 or 1/4 ton size, it would automatically match the refrigerant flow to the heat flow for you.

I am actually considering doing the repurposed auto A/C condenser thing with a unit I have. I look forward to seeing your results.

[ecomodded]

I want to use the car's AC condenser as the heat pumps evaporator , I have confused the parts in the conversion from AC to heat pump , everything is reversed , twice it seems at times..

A 1/4 ton expansion valve is about 3000 Btu's , will this limit the system to that amount ? If so I think it might be better to use the 1/3 ton TXV and try to max it out ? I still know next to nothing about the expansion valve so bear with me.

[jeff5may]

A TXV acts as a fixed orifice above a certain temperature, usually 60 to 70 degF. Below that temp, it matches the flow based on bulb pressure (which follows evaporator exit temperature) vs evaporator pressure. Some valves are preset to add a fixed amount of superheat, where others have a superheat adjustment. The closer the charge in the bulb is to what's in your system, the better the txv will track and maintain a constant superheat.

The rated value on the valve is about 2/3 of the full-bore capacity of the valve. A 1/3 ton valve can open up to pass 1/2 ton of capacity. If you oversize the valve, it will overshoot its target and cause oscillation, or "hunting".

[ecomodded]

I should or will use with the 1/4 ton valve , nice to know they have some headroom for those moments of high efficiency weather.

For the fans I am thinking of a few automotive 12v radiator fans or a large 2 fan set , for fan speed a cheap 20A variable PWM speed controller.

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I have the condenser off its bolts and connectors but it it hung up on something I cannot see, its looking like I will have to do the by the book and remove the Inner wheel wells then the bumper skin and bumper and finally the Condenser.

If the front clip does need to come off I will cut a hole in it to pass more airflow over the side mount intercooler before reinstalling it , something I wanted to do regardless of the Condenser removal. This condenser is coming off